Identification of candidate MLO powdery mildew susceptibility genes in cultivated Solanaceae and functional characterization of tobacco NtMLO1.

Michela Appiano,Luigi Ricciardi,Domenico Catalano,Richard G F Visser,Valentina Bracuto,Zheng Zheng,Stefano Pavan,Concetta Lotti,Yuling Bai

doi:10.1007/s11248-015-9878-4

Abstract

Specific homologs of the plant Mildew Locus O (MLO) gene family act as susceptibility factors towards the powdery mildew (PM) fungal disease, causing significant economic losses in agricultural settings. Thus, in order to obtain PM resistant phenotypes, a general breeding strategy has been proposed, based on the selective inactivation of MLO susceptibility genes across cultivated species. In this study, PCR-based methodologies were used in order to isolate MLO genes from cultivated solanaceous crops that are hosts for PM fungi, namely eggplant, potato and tobacco, which were named SmMLO1, StMLO1 and NtMLO1, respectively. Based on phylogenetic analysis and sequence alignment, these genes were predicted to be orthologs of tomato SlMLO1 and pepper CaMLO2, previously shown to be required for PM pathogenesis. Full-length sequence of the tobacco homolog NtMLO1 was used for a heterologous transgenic complementation assay, resulting in its characterization as a PM susceptibility gene. The same assay showed that a single nucleotide change in a mutated NtMLO1 allele leads to complete gene loss-of-function. Results here presented, also including a complete overview of the tobacco and potato MLO gene families, are valuable to study MLO gene evolution in Solanaceae and for molecular breeding approaches aimed at introducing PM resistance using strategies of reverse genetics.Electronic supplementary materialThe online version of this article (doi:10.1007/s11248-015-9878-4) contains supplementary material, which is available to authorized users.

Highlights

Powdery mildew (PM) is a major fungal disease affecting thousands of plant species, caused by ascomycete fungi belonging to the order of Erysiphales (Glawe 2008)
In order to characterize NtMLO1 at the functional level, we set up an assay based on its transgenic overexpression in the previously described tomato line Slmlo1, which carries a loss-of-function mutation in the tomato SlMlo1 homolog and is resistant to the PM fungus O. neolycopersici (Bai et al 2008)
We functionally characterized tomato SlMLO1 and pepper CaMLO2 as two solanaceous Mildew Locus O (MLO) susceptibility genes, as their inactivation was causally associated with PM resistance (Bai et al 2008; Zheng et al 2013)

Summary

Introduction

Powdery mildew (PM) is a major fungal disease affecting thousands of plant species, caused by ascomycete fungi belonging to the order of Erysiphales (Glawe 2008). Mlo resistance has been later shown to occur in other plant species as well, Arabidopsis, tomato, pea, pepper and bread wheat (Bai et al 2008; Buschges et al 1997; Consonni et al 2006; Humphry et al 2011; Pavan et al 2011; Wang et al 2014; Zheng et al 2013) This eventually led to the formalization of a breeding approach based on the systematic inactivation of MLO susceptibility genes across cultivated species affected by the PM disease (Dangl et al 2013; Pavan et al 2010, 2011). Loss-of-function mutations of barley HvMLO confer resistance to all known isolates

Methods

Results

Conclusion